In regards to AFM, we have an 08 Impala w/3.9 v6 AFM. You set the DIC for instant fuel mileage & watch it change back & forth between 3 & 6 cyl mode. It changes back to 6 with the slightest of throttle pressure increase whether accelerating or a slight increase in grade. I don't see how you could experience a lack of performance at any time, just hit the throttle. Also the switch back & forth is almost imperceptable. The only way I can feel it is if I lean my head against the window glass. I would think a v8/v4 would be even smoother.